The primary aim of this study is to test the feasibility of implementing, in multiple states, a population-based sampling strategy for a mobile population the children of agricultural labor migrants along the eastern United States seaboard. Agricultural labor migrants number in the millions and are one of the United States'most mobile populations. In addition to heightened quantitative mobility, they have qualitative migration patterns that are both trans- and intra- national. Building upon a successful pilot study in one state, this study will implement a population-based sampling strategy for families with children in three states. Key to the sampling strategy is the fact that labor migration is not random. Labor migrants predictably move across well-established migration portals, and their housing locations are well-known. We propose a multistage cluster sample to: 1) identify the migration portals in each state;2) stratify counties in each portal by the density of labor migrants;3) randomly sample a fraction of counties per density stratum;and 4) in each selected county, randomly sample a fraction of addresses where migrants live. Our innovative sampling strategy will yield representative data about agricultural U.S. migrants, a highly vulnerable and understudied population. Our secondary aim is to test the independent association between family migration patterns and child health care access, including both realized (health services use) and potential (barriers to care) health access outcomes. To guide the analysis, we augment the widely-used Behavioral Model of Health Services Use (Andersen 1995). One key question is whether or not the type of family migration pattern, e.g. whether trans- national or intra-national, is associated with health services use and barriers to care, after controlling for numbers of moves, health needs, predisposing factors, and enabling resources. The significant contributions of this project are: 1) introduction of a replicable population-based sampling strategy for a mobile population, and 2) advancement of knowledge about how population movement is associated with children's access to health care (PA-00-32). This project is important to public health because many parents and children in this population are undocumented immigrants a sizeable and growing U.S. population about whom little is known. Project Narrative: The significant contributions of this project are: 1) the introduction of a replicable population-based sampling strategy for a mobile population, and 2) advancement of knowledge about how population movement is associated with access to health care for children (PA-00-32). This project is important to public health because a large proportion of parents and children in this population are undocumented immigrants-a sizeable and growing U.S. population about whom little is known-results from this project can advance knowledge about these families.